A fundamental question in auditory neuroscience is how neural activity in the cerebral cortex gives rise to perception and how changes in brain activity relate to different behavioral states. Activity in primary auditory cortex has been shown to be modulated by engagement in a psychophysical task, but relatively little is known about the causal links between neural activity and perception and how different behavioral states modulate various cortical areas at both the single neuron and population level - especially for non-primary auditory areas. The experiments in this proposal will use a powerful combination of multi-channel neurophysiological techniques and behavioral testing to examine the links between neural activity in auditory cortex and perception at both the individual neuron and population levels in marmosets. Specific Aim 1 examines and compares behavioral modulation of neural responses between two auditory cortical areas. Specific Aim 2 focuses on the correlation between neural responses and marmoset's perception of pitch-bearing harmonic complex tones in the pitch region of auditory cortex. Results of the experiments described here will contribute greatly to our understanding of the perceptual organization of complex sounds and their physiological underpinnings in marmosets. These experiments will also help to elucidate the functional organization of different levels of the auditory cortical hierarchy. Finaly, because of the close phylogenetic relationship between human and nonhuman primates, these results will provide a better understanding of complex sound processing, including speech perception, in human auditory cortex.